The present invention relates to a solid soap composed mainly of a hard and elastic gel of corn starch--soap--water, and its relevant manufacturing process.
Conventional solid soaps are normally composed of about 85% anhydrous soap (mainly sodium salts of higher fatty acids) 10-13% water and the usual additives.
The soaps composed according to these formulae have several drawbacks. In fact a great part of the active ingredient (soap in this case, and up to 50% of it) is useless for detergency, so causing high production costs.
Moreover this excess of active ingredient is harmful because of the excessive degreasing action on the skin (the so-called alkaline effect). On the other hand attempts to overcome the drawback of the high cost through use of soap containing higher water contents did not give positive results. In fact these soaps when used, produced abundant slough, undergoing at the same time a loss in firmness.
Several types of additives, drying materials and fillers were tried in the attempt to overcome these drawbacks. One of these materials is starch, which is known as a filler. The addition of starch made in the previous techniques was made in such a way as to prevent the formation of gels and dextrins because of possible difficulties in the making and finishing of the product.
It has now been surprisingly found that a soap including a hard and elastic gel composed of:
starch, 8 to 28% by weight, PA1 water, 10 to 60% by weight, PA1 sodium and potassium salts of higher fatty acids, 24 to 54% by weight, PA1 starch, 8 to 28% by weight, PA1 sodium and/or potassium salts of higher fatty acids, 24 to 54% by weight, PA1 water, 10 to 50% by weight. PA1 obtainment of a hard and elastic gel with a minimum supply of heat; PA1 low consumption of the product in use; PA1 resistance to water; PA1 dermatologic characteristics of the product taking into account the favourable effect of the starch and the unfavourable effect of the soap; PA1 capacity of bonding large amounts of water to the gel; PA1 characteristics of foam, appearance, pleasant feeling to the touch; PA1 capacity to include several additives such as, for instance, perfumes and colouring matters without weakening the gel structure. PA1 100 to 0 Na.sup.+ /K.sup.+ up to 30 to 70 Na.sup.+ /K.sup.+
can overcome the above mentioned drawbacks.
Gels are rigid or semi-rigid colloids that contain high quantities of liquid substance, usually water, and in which the constituent particles are bonded together in reticular structures. Gels can therefore be considered as solid matter, more or less plastic. Then can be classified into two classes, elastic and non-elastic. Partial desolvation of the first ones brings about the formation of an elastic solid, while in the second class, partial desolvation brings about a loss of elasticity and possible pulverization and/or vitrification of the gel.
Soaps are generally alkaline salts (sodium and potassium) of higher fatty acids (lauric, myristic, palmitic, oleic, stearic and others). They are formed by the reaction (saponification) of the esters of the fatty acids with glycerol and alkalies. These soaps can be classified as: soft soaps, derived from reaction with potassium alkalies, hard soaps, derived from reaction with sodium alkalies.
Starch is a carbohydrate made by molecules with linear or branched chains, mainly associated in micelles by hydrogen bonds or molecular water bridges.
By supplying heat to a suspension of water and starch, the reticular structure of starch weakens because of disruption of the hydrogen bonds. Heat brings about hydrolysis of the micelles and therefore an irreversible gelatinization together with the swelling of the micelles due to the water molecules becoming attached to the liberated hydroxyl groups. It is also known that if this reaction is carried out together with fatty acids or soaps containing fatty acids, the latter form complexes with the linear fraction of the starch, so creating cross bonds between macromolecules, bonds which reinforce remarkably the gel structure.